The present invention relates to a machine for printing objects substantially having shapes of revolution of the type comprising:
means for transporting objects to be printed between at least one station for loading objects on said transport means and a station for unloading said objects from said transport means,
at least one printing station arranged between the loading station and the unloading station, said printing station comprising at least four printing units arranged to project ink on the objects to be printed so as to print said objects, each printing unit projecting ink of a different color so as to make up a four-color process,
means for transferring an object to be printed from the transport means to the printing station and from the printing station to the transport means.
Document EP-1 918 100 describes a printing machine in which a plurality of mandrels supporting objects to be printed are provided on a rotary plate to pass in front of a series of processing stations for the object to be printed, including a printing station. Each mandrel can move between a transfer position, in which the mandrel is moved with the rotary plate from one processing station to the other, and a printing position, in which the mandrel is positioned opposite printing units of the printing station and is rotated around its axis to expose a printing area of the object to be printed to the different ink jets coming from the printing units.
In the printing position, a handle for rotating the mandrel engages with a driving guide rotated by a drive motor so as to rotate the mandrel around its axis. Due to the mechanical and machining allowances of the mandrels and said driving means, it is very difficult to ensure identical positioning and a constant speed of rotation for all of the mandrels that pass in front of the printing station. Thus, from one mandrel to another, the positions of the objects supported by said mandrels and their rotational speed profile can be substantially different. Each printing unit comprises a plurality of inkjet nozzles arranged in two lines parallel to the axis of rotation of the mandrel and spaced apart by a small distance, for example 0.075 mm, in a direction substantially perpendicular to the axis of rotation of the mandrel. The two lines of nozzles must project ink onto a same line of the printing zone of the object to be printed, i.e. the inkjets of the two lines must converge on the surface of the object to be printed.